1. Field of the Invention
The present invention relates generally to fluid flow control valves provided with means for reducing and minimizing the noise which such valves produce as fluid flows therethrough. Specifically, the invention relates to the type of such valves which are known as low noise valves, wherein the valves themselves are constructed to operate at lower noise levels than corresponding valves of ordinary construction. More specifically, the invention relates to that form of low noise valve wherein the control of the fluid pressure drop across the valve, and the control of the rate of fluid flow through the valve, are effected by the use of perforated or equivalent members which impose controllable fluid restrictions along the fluid flow path through the valve, and wherein a degree of noise reduction is effected by dividing the restrictions and resulting pressure drop into sequential stages.
2. Description of the Prior Art
Numerous constructions have been suggested in the past for effecting valve noise reduction and minimization. The more popular ones of those constructions have included the sequential restriction and pressure drop low noise valve construction noted above, a similar arrangement wherein a diffuser is added to a valve downstream of the valve's internal restriction, and the arrangement wherein a muffler is attached to the outlet priping of a valve. Each of these three known constructions will now be briefly described.
The above-noted low noise valve construction including sequentially disposed perforated or equivalent members providing sequential stages of restriction and pressure drop is known in the art in several forms. Typical of such constructions are the double cage valve construction which is disclosed in the Curran U.S. Pat. No. 3,648,718, the stacked disc valve construction which is disclosed in the Barb U.S. Pat. No. 3,894,716, the reacting stream valve construction which is disclosed in the Myers U.S. Pat. No. 3,990,475, and the spaced disc valve construction which is disclosed in the Engel et al U.S. Pat. No. 4,024,891. In each of such valve constructions, a plug is movable to vary the effective area of the valve flow path by varying the area, and hence the restricting and pressure-dropping effect, of the restrictions, thereby to provide the above-noted control of the fluid pressure drop across the valve and the rate of flow of fluid through the valve.
The principle which is responsible for the noise reduction which is achieved in each of the noted forms of low noise valves is that, if the total restriction and pressure drop present in such a valve is divided or broken down into two or more portions or stages or restrictions acting in sequence or series, the sum of the noises individual to the several series restrictions or stages is significantly less than the noise which would be produced for the same fluid flow and pressure drop conditions if the restriction were not so divided, and hence if all of the pressure drop occurred across a single restriction. For example, according to this principle, a given fluid flowing at a given rate through a valve and experiencing a pressure drop will produce significantly less noise if the given pressure drop occurs across two restrictions in series, as distinguished from occurring across a single restriction of a size required to produce the same pressure drop.
For convenience, the term restriction as used herein identifies each arrangement or stage which effects one of the series pressure drops in a low noise valve as described above, notwithstanding the fact that such a restriction may well actually be in the form of a plurality of perforations, apertures, or fluid passageways acting in parallel on the fluid flow. The total restriction present in such a valve for any given plug position is thus the sum of the individual series restrictions or stages, or simply the sum of the restrictions as defined above.
Also for convenience, any such a valve as described above, including means to divide its total restriction and pressure drop into two or more series stages to effect noise improvement, reduction, or minimization, will be referred to hereinafter simply as a low noise valve. Further, a valve of the same nominal size as a given low noise valve but not including such dividing of its restriction into stages will be referred to hereinafter as the standard counterpart of the given low noise valve.
In the diffuser arrangement referred to above as the second of the more popular noise reducing constructions, a diffuser, which is usually in the form of a perforated closed end tube or chamber, is placed on the downstream side of an existing valve. The diffuser functions to reduce noise in much the same way as does an additional stage of restriction within a low noise valve as described above.
The known forms of low noise valves, operating according to the above-noted divided pressure drop principle, have indeed operated at lower noise levels as compared to their standard counterparts. Similarly, the noted practice of adding a diffuser to a valve has generally been effective to reduce the noise produced by the valve. However, noise reduction to greater extents than those provided by the known arrangements is required or desired in many applications. Heretofore, it has been necessary to add additional pressure dropping stages in the process of obtaining such desired additional noise reduction, with the resultant undesirable increase in the size, complexity, and cost of the valve structure. The attachment of diffusers to valves has the further disadvantage of requiring hardware exterior of the valves.
In the third of the known constructions referred to above, wherein a muffler is located on the downstream side of a valve, noise energy is changed into heat energy as the fluid and noise pass through the filling material of the muffler. However, this procedure for reducing valve noise has the disadvantages of subjecting the fluid to the muffler material, of the clogging and/or contaminating of the muffler material by the fluid, and of requiring an extra piece of hardware exterior of the valve.